1. Field of the Invention
The present invention relates generally to cardiac stimulation and, more particularly, to an implantable endocardial lead assembly having one or more stents.
2. Description of the Related Art
For a variety of reasons, a person's heart may not function properly and, thus, endanger the person's well-being. Medical devices have been developed to facilitate heart function. For instance, if a person's heart does not beat properly, a cardiac stimulator may be used to provide relief. A cardiac stimulator, such as a pacemaker or a cardioverter/defibrillator, is a medical device that delivers electrical stimulation to a patient's heart. A cardiac stimulator generally includes a pulse generator for creating electrical stimulation impulses and at least one conductive lead having an electrode at one end for delivering these electrical stimulation impulses to the designated portion of the heart.
There are generally two types of implantable leads used with cardiac stimulators. One type requires surgical opening of the patient's chest wall to expose the heart. The electrode is then attached to an outer portion of the heart. The other type of lead is inserted endoscopically through a body vessel, such as a vein, and directed into the heart. The distal end of the electrode is disposed within the heart near the myocardial tissue to be paced.
Existing endocardial leads have a lumen and an electrode having a closed tip coupled to the lead's distal end. Prior to transvenous insertion, a flexible stylet is disposed in the lumen so that the distal end of the stylet abuts the interior surface of the closed tip of the lead. The lead and the stylet are then inserted transvenously as a unit. The movement and positioning of the lead is accomplished by manipulating the proximal end of the stylet. After the distal end of the lead has been successfully positioned in or near the heart, the stylet is removed, and the proximal end of the lead is connected to a cardiac stimulator.
One or more leads may be positioned at various places in the heart, depending upon the type of pacing desired. Transvenous pacing of the left atrium and the left ventricle via the coronary sinus has become popular for both diagnosis and therapy of cardiac arrhythmias. The coronary sinus has five major venous tributaries that can be entered by pacing leads. The most common placement involves lodging the lead's electrode in the great cardiac vein. However, many patients require a more esoteric placement of the lead, such as, for example, in the anterior interventricular vein.
Lodging an electrode in a body vessel, such as the coronary sinus or one of its tributaries, can be quite difficult. This difficulty arises from the fact that most existing electrodes are designed to attach to an inner surface of a chamber of the heart, rather than the inner surface of a body vessel. Some leads, for instance, use electrodes that terminate in a corkscrew-shaped protuberance that is designed to screw into myocardial tissue. However, because this corkscrew is placed on the end of the electrode, it is difficult to attach it to walls of a body vessel that run parallel to the lead. By way of another example, some electrodes include angled tines that protrude radially from the electrode. Although these tines can often be used to lodge the electrode in a body vessel, the tines tend to occupy a significant amount of the flow path through the body vessel. As such, blood flow through the body vessel may be restricted.
There are also certain disadvantages associated with a lead having a closed end, particularly when placing the lead in the coronary sinus or one of its tributaries. Aside from the potential for venous occlusion, existing leads are implanted by the simultaneous manipulation of the lead and the stylet disposed within the lead. These leads may have diameters that begin to approach the diameters of the coronary sinus or its tributaries. Thus, such leads may be difficult to position by manipulating a stylet disposed therein. The difficulties of the implantation procedure may be further exacerbated by the presence of plaque or other obstructions in the coronary sinus or its tributaries.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the foregoing disadvantages.